1. Technical Field
The present invention relates to a backflow prevention valve having a valve plug disposed opposite a port formed in the valve plug seating surface, and causes the valve plug to deform elastically according to fluid pressure to open and close the port, and relates more particularly to a backflow prevention valve that can suppress an increase in path resistance and a drop in the flow rate even when the valve port is formed at an eccentric position. The invention also relates to a fluid discharge device that has this backflow prevention valve disposed in the fluid path.
2. Related Art
Constructions that have a support orifice supporting the valve plug and a fluid port through which fluid flows formed in the valve plug seating surface, have the valve plug disposed opposite the fluid port, and elastically deform the valve plug according to the fluid pressure from the fluid port side and the fluid pressure from the opposite side to open and close the fluid port are used as backflow prevention valves because of their simple, compact construction.
Japanese Unexamined Patent Appl. Pub. JP-A-2009-108967 teaches a backflow prevention valve that has an umbrella-like valve plug supported in a support orifice formed in the center of the valve plug seating surface of the valve seat. In JP-A-2009-108967, fluid ports are formed at equal angles around the support orifice in the valve plug seating surface, and adjacent ports communicate through a communication channel. By providing this communication channel, fluid can flow from the edge of the umbrella even where only the communication path is formed, the sectional area of the fluid path can thus be increased, and pressure loss can be reduced.
Because where the ports are formed is not specifically limited with the backflow prevention valve taught in JP-A-2009-108967, a plurality of ports can be disposed evenly in the circumferential direction around the support orifice. With this backflow prevention valve, however, there are situations in which ports cannot be disposed wherever desired in the sealed area that is sealed by the umbrella of the valve plug (the circular area surrounding the support orifice) due to installation space requirements. In such situations fluid flows from the part of the sealed area eccentric to the center of the support orifice (the area where the fluid port is formed), but there is substantially no flow where the ports are not formed. Path resistance therefore increases and pressure loss increases.
In addition, because the flow rate drops where the ports are not formed, bubbles grow where the flow rate is low when a fluid that contains bubbles flows, and large bubbles can grow easily. The bubbles therefore do not flow easily, interfere with smooth fluid flow, and can adversely affect flow on the downstream side of the backflow prevention valve. For example, if this type of backflow prevention valve is disposed in the fluid supply path of a fluid discharge device, fluid discharge quality drops as a result of fluid containing large bubbles being supplied to the fluid discharge head.